Microbat is the common name for any of the bats comprising the suborder Microchiroptera of the order Chiroptera (bats), characterized by true wings and flight (as with all bats), lack of claws on the second digits, lack of underfur, and ears that generally have large pinnae and do not form a closed ring, but rather have edges that are separated from each other at the base of the ear. Unlike most members of the other group of bats, the megabats comprising the suborder Megachiroptera, the microbats use sophisticated echolocation for orientation.

Mircrobats also are known as "insectivorous bats," "echolocating bats," and "small bats." All these names are somewhat inaccurate, because not all microbats feed on insects, there is one genus of megabats that use a simple (but unrelated) form of echolocation, and some microbat species are larger than small megabats.

Microbats provide a valuable role in the ecosystem through limiting prey populations and through themselves serving as prey to various mammals, snakes, birds of prey (such as owls nd hawks), and even other bats. They are particularly vulnerable as they roost or emerge in large groups from their protected roosts; while flying alone they are difficult to catch.

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Bats are often looked at as harmful pests, and they may be an annoyance when they roost in buildings, such as homes, or because of the danger of transmitting rabies to cattle or, more rarely, humans. However, they are also beneficial, by removing pest insects, which themselves may transmit disease or destroy crops. In addition, feces is collected from caves for commercial use as fertilizer.

Overview and description

Bats comprise the mammalian order Chiroptera and traditionally are divided into the two distinct groups, typically suborders, of Microchiroptera, or microbats, and Megachiroptera, or megabats. Although these names imply that microbats are smaller than megabats, this is only true in a general since, as some microbat species are larger than some megabat species. However, there remain consistent differences in other physical and ecological aspects.

Among distinctions between the two suborders is that microbats lack the underfur characteristic of megabats and have only guard hairs or are naked; microbats lack the claw at the second toe of the forelimb which is characteristic of all but one of the megabats; and the ears of microbats tend to have large, complex pinnae (external ear)s that include an enlarge tragus or antitragus (Wund and Myers 2005). In addition, microbats tend to have small eyes, while megachiropterans tend to have large prominent eyes. Furthermore, the dentition or cheek teeth of microbats generally can easily be related to dilambdodont teeth, whereas megabats have simplified cheek teeth that are difficult to interpret (Wund and Myers 2005). And, as a major distinction, microbats use echolocation, whereas megabats do not typically, with the exception of members of the genusRousettus, which have a simplified, unrelated form of echolocation.

There also are important ecological differences, as megabats typically are herbivorous, consuming fruit, nectar, and pollen, while microbats often are insectivorous, but also have a variety of other feeding behaviors.

Microbats typically are 4 to 16 centimeters (1.5 to 6 inches) long. The smallest bat is the microchiropteran Craseonycteris thonglongyai, which is about the size of a large bumblebee and may be the world's smallest mammal. It weighs only 2 to 3 grams and has a head and body length of 29 to 33 millimeters (1.1 to 1.3 inches), and a forearm length that ranges from 22 to 26 millimeters (0.9 to 1.0 inches)(Goswami 1999; Wund and Myers 2005).

Microbats have a wider distribution than the Old World megabats and are found in both the Old World and New World. Little brown bats, Myotis lucifugus, which are abundant in North America, from the Pacific to the Atlantic coasts, are known to live for decades. One individual that was banded and recaptured had been living for 33 years when it was recaptured (Wund and Myers 2005).

Bats do not seem to use echolocation directly in communicating with one another. Instead, they employ a variety of calls, most of which are audible to humans. In addition, they use pheromones and scent marks for such purposes as communicating reproductive status and individual or group identity. In addition, visual displays may be used, including during courtship to attract mates (Wund and Myers 2005).

Only 0.5 percent of bats carry rabies. However, of the few cases of rabies reported in the United States every year, most are caused by bat bites (Gibbons and Rupprecht 2000).

Diet

Most microbats feed on insects and are able to catch them while flying or while the insects are on a surface. Many species of microbats have chitinase enzymes in their intestines that are produced by symbiotic bacteria. These help in digesting the insect prey (Whitaker et al. 2004).

However, microbats also employ a variety of other feeding behaviors. Some of the larger species hunt vertebrates, including birds, rodents, lizards, frogs, or even fish. They also consume other bats.

Vampire bats are microbats that feed on the blood of mammals or birds. There are three species that feed solely on blood: The common vampire bat (Desmodus rotundus), the hairy-legged vampire bat (Diphylla ecaudata), and the white-winged vampire Bat (Diaemus youngi). All three species are native to the Americas, ranging from Mexico to Brazil, Chile, and Argentina. Vampire bats use their sharp teeth (incisors) to make incisions in the skin of their prey, which for the common vampire bat is mammalian prey, but for the other two species is the blood of birds. Vampire bats have a short, conical muzzle and lack a nose leaf, and the common vampire bat has specialized thermoreceptors on its nose, which aids the animal in locating areas where the blood flows close to the skin of its prey. The digestive system of vampire bats is adapted to their liquid diet, and their saliva contains a substance, draculin, which prevents the prey's blood from clotting. The vampire bats do not suck blood, but rather lap the blood at the site of the hemorrhage.

Echolocation

Bats are one of the most famous examples for echolocation among animals. All microbats use echolocation. The only megabat which is known to echolocate is the genus Rousettus, which uses a different method of echolocation than that used by microbats. The echolocation system of bats is often called biosonar.

Microbats generate ultrasound via the larynx and emit the sound through the nose or the open mouth. Microbat calls range in frequency from 14,000 to over 100,000 hertz, well beyond the range of the human ear. (Typical human hearing range is considered to be from 20Hz to 20,000 Hz.) The emitted vocalizations form a broad beam of sound that is used to probe the environment.

Bat calls very in duration and structure, with some species using short calls (2 to 5 milliseconds) that are frequently repeated, while other species use longer calls (20 milliseconds or so) with a lesser rate of repetition (Wund and Myers 2005).

Some moths have developed a protection against bats. They are able to hear the bat's ultrasounds and flee as soon as they notice these sounds, or stop beating their wings for a period of time to deprive the bat of the characteristic echo signature of moving wings, which it may home in on. To counteract this, the bat may cease producing the ultrasound bursts as it nears its prey, and can, thus, avoid detection.

Classification

There are about 17 families with almost 800 species of microbats, typically organized into seven superfamilies. Following is the classification according to Simmons and Geisler (1998):

Simmons, N. B., and J. H. Geisler. 1998. Phylogenetic relationships of Icaronycteris, Archeonycteris, Hassianycteris, and Palaeochiropteryx to extant bat lineages, with comments on the evolution of echolocation and foraging strategies in microchiroptera. Bulletin of the American Museum of Natural History 235: 1-182.

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